MONDAY, July 2 (HealthDay News) -- Babies born on the early side of full-term may have higher odds of academic delays than those delivered a week or two later, new research finds.
Experts aren't sure what exactly causes the achievement lag, evident in third grade. "Perhaps there is something about the uterine environment that supports brain development in a favorable way in the last month of pregnancy and perhaps gets disrupted by earlier birth," said study leader Kimberly Noble, assistant professor of pediatrics at Columbia University Medical Center and New York Presbyterian Hospital in New York City.
The study looked at data from more than 128,000 births of single babies born between 37 and 41 weeks, the span considered full term. When the children reached third grade, the researchers examined their scores on standardized tests to see if their delivery date suggested a difference in learning ability. They concluded that it did.
The math and reading scores of children born technically at full-term -- 37 to 38 weeks' gestation -- lagged slightly behind their peers born just a little later, at 39, 40 or 41 weeks.
The study is published online July 2 in Pediatrics
For years, experts have known that children born preterm, defined as before 37 weeks, are more likely to have academic difficulties, Noble said. Until recently, less attention has focused on differences between children born early full term or later full term.
The commonly held belief that babies born anytime between 37 and 41 weeks develop similarly may be inaccurate, she writes.
The differences found were relatively small, Noble said, but enough to make a difference from a public health or population point of view.
Compared to children born at 41 weeks, those born at 37 weeks had a 23 percent higher risk of moderate reading impairment. Those born at 38 weeks had a 13 percent increased risk.
Math scores indicated a 19 percent higher risk of moderate impairment for children born at 37 weeks compared to the 41-week babies. For those delivered at 38 weeks, the risk of a mild impairment was 11 percent higher.
Why the difference? "We don't know for sure from this data," Noble said. However, it is known that during the final weeks of pregnancy, the brain grows rapidly and there is an increase in gray matter and white matter and brain cell differentiation, she said.
The association held when she took into account other factors known to affect school performance, such as maternal education and income level. However, this link between earlier delivery and learning delays does not prove a causal relationship.
But Noble said parents and doctors considering early, elective C-sections might consider the research findings before scheduling.
Dr. Roya Samuels, a pediatrician at Cohen Children's Medical Center in New Hyde Park, N.Y., said the study findings may change the tendency of parents and doctors to think of all full-term babies alike.
"The longer an infant is incubated, it looks like the more synapses [brain connections] are able to be created and the more advanced the neurological growth is," said Samuels, who was not involved in the study.
She predicted that more research will focus on the crucial last weeks of pregnancy.
As for whether this research should affect early, elective C-section deliveries, Samuels said, "that is a tough one." Many are scheduled because of impending danger to the mother or infant, she said.
For now, the message for pregnant women, she said, is "to take the best prenatal care of themselves they possibly can."
To learn more about healthy pregnancies, visit March of Dimes.
SOURCES: Kimberly G. Noble, M.D., Ph.D., assistant professor, pediatrics, Columbia University Medical Center and New York Presbyterian Hospital, New York City; Roya Samuels, M.D., pediatrician, Cohen Children's Medical Center, New Hyde Park, N.Y.; August 2012 Pediatrics
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